Integrated circuits are usually produced from large wafers of semiconductor material such as, for example, silicon or gallium arsenide, from which a plurality of chips can be simultaneously produced. The dimensions of the individual chips are delineated by scoring or grooving the wafer in checkerboard fashion. Each chip is provided with a circuit pattern by using standard masking and photolithographic methods to form an integrated circuit. Contact-holes are also provided for connecting between different conductive layers on a circuit.
The conductive film or metallization typically serves to electrically connect together the devices of an integrated circuit, to connect one integrated circuit to another, to allow access from outside the circuit and to form electrodes for devices. The metal most commonly used for metallization is aluminum. The aluminum can be deposited on the semiconductor wafer using any one of a variety of conventional deposition techniques, such as, for example, sputtering or evaporation. Copper can be used as an alternative to aluminum for interconnections.
Conventional metallization involves several steps preparatory to actually depositing the aluminum layer. A barrier layer can be deposited first after a contact opening is formed, if desired, to prevent the aluminum from dissolving silicon from the substrate layer, a problem referred to as "spiking." Where copper is used as the interconnect layer, a barrier layer is used to prevent the copper from diffusing into the silicon substrate which will deteriorate the performance of transistor properties.
FIGS. 1A through 1F, show a common process for forming a multi-layer metal interconnect structure. A conducting layer 100 of doped silicon or other material is provided and covered with an insulating layer 102, such as SiO.sub.2 or Si.sub.3 N.sub.4 as shown in FIG. 1A. A contact hole 104 is formed through the insulating layer 102 using conventional photolithographic techniques to expose a portion of the conducting layer 100.
FIG. 1B shows a barrier layer 106 formed over the surface of the structure of FIG. 1A. A barrier layer 106 is provided when the potential for aluminum spiking or copper diffusion into silicon can cause a failure. Typically, the barrier layer 106 is deposited onto the bottom of the contact opening. The barrier layer 106 is typically a compound of titanium-tungsten or titanium nitride and is very thin, on the order of 50-200 .ANG. at the bottom. The barrier layer processing step shown in FIG. 1B is optional and its use depends upon the materials being used.
The next conventional step includes forming an adhesion layer 108 of a refractory metal, typically, titanium. Other materials include tungsten germanium and silicon. The adhesion layer provides for good adhesion of a subsequently deposited aluminum layer to the surface of the semiconductor wafer, including any dielectric materials which may have been deposited. This layer is typically 20 to 500 .ANG. thick at the bottom of opening 104.
Next, a layer of aluminum or copper 110 is formed, typically by sputter deposition at a temperature between room temperature and 200.degree. C. as shown in FIG. 1D. The aluminum layer can be formed of an aluminum alloy such as 1% silicon and/or 0.5% copper. Unfortunately, the deposition steps required for FIGS. 1C and 1D require separate deposition chambers to avoid contamination, the necessity of changing the target and other related deleterious factors. Such methods have dedicated deposition chambers for each layer. These chambers are mounted to a central vacuum transfer chamber, so that the layers are not exposed to any ambient, other than vacuum, typically in the range of IE-9 to IE-7 Torr, during transfer from one chamber to the next.
As shown in FIG. 1D, the step coverage of the aluminum aluminum alloy, copper or copper alloy layer can be poor. To improve the step coverage, heat is applied in the step of FIG. 1E in excess of 300.degree. C. and typically in the temperature range of 400.degree. C. to 600.degree. C. This anneal step may be performed in the deposition chamber or in a separate anneal chamber. This causes the aluminum or copper layer 110' to flow and form an alloy layer 108' of the material deposited as the adhesion layer 108 and the aluminum or copper 110 as shown in FIG. 1E. During this heating step, a limited portion of the aluminum combines with the refractory metal to form an aluminum/refractory alloy 108'.
Lastly, additional aluminum or copper is deposited in a third deposition step which combines with the reflowed aluminum or copper layer 110' to form a thicker aluminum or copper layer 110" and thereby reduce the electrical impedance of this metal layer as shown in FIG. 1F.
An alternative process sequence has been the deposition of a thin aluminum or copper layer 110, typically 500 to 4000 angstroms. At temperatures less than 300.degree. C. as in FIG. 1D, followed by deposition of a hot aluminum or hot copper layer 111 at temperatures between 400 and 600.degree. C., FIG. 1E, during this hot step, part of layer 110 combines with layer 108 (FIG. 1D) to form a composite alloy layer 108' (FIG. 1E). This allows for the hot aluminum or hot copper layer 112 to flow into the opening 104. The hot aluminum or hot copper deposition can be continued until a fully planarized surface is obtained, FIG. 1F.
These processes are time consuming, and require the use of at least three different deposition chambers in order to complete a single metallization. (Four deposition chambers are needed if a barrier layer is included in the process.) Accordingly, the need exists for a process which reduces the time and equipment required to produce metallization on a semiconductor wafer.